Re: Current Limiting and Impedence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: robert heidlebaugh <rheidlebaugh@xxxxxxxxxxxxxx>

Paul: I have used cores like you have just stacked insite thin PVC pipe
clamped tight , and glued into a rod with fiber glass resin to make ferrite
antenna rods 1 meter long good to over 30 Mhz. The trick is to stack them
tight with little or no air gap. Dont try to grind them. Ive tried that.
They just kill your grinder with all the ceramic binder in them. Yes I have
the tools to grind then, Im an assayer and I grind rocks, but cores are
tough to grind and eat equipment.
    Robert   H
--


> From: "Tesla list" <tesla@xxxxxxxxxx>
> Date: Fri, 13 May 2005 11:53:35 -0600
> To: tesla@xxxxxxxxxx
> Subject: Re: Current Limiting and Impedence
> Resent-From: tesla@xxxxxxxxxx
> Resent-Date: Fri, 13 May 2005 11:59:21 -0600 (MDT)
>
> Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>
>
> Malcolm,
> You mention N27 ferrites but the ferrites I have access to are surplus and
> completely unmarked and of unknown origin. The good thing is that I have a
> bucketload of them that have accumulated from various sources over many
> years. I believe that most of them are ferrite beads that were on power
> cords. Would these work in use as you suggested, crushed up in a PVC tube?
> I like this idea as I have ready access to so many ferrite beads. Since it
> sounds so good, I just know you are going to tell me that they are
> completely different from the ferrite used for toroids and transformers and
> therefore useless for this application. {:-(
> Regards.
> Paul
> Think Positive
>
> ----- Original Message -----
> From: "Tesla list" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
> To: <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
> Sent: Thursday, May 12, 2005 4:46 PM
> Subject: Re: Current Limiting and Impedence
>
>> Original poster: "Malcolm Watts"
> <<mailto:m.j.watts@xxxxxxxxxxxx>m.j.watts@xxxxxxxxxxxx>
>>
>> On 12 May 2005, at 10:27, Tesla list wrote:
>>
>>> Original poster: "Gerald  Reynolds"
> <<mailto:gerryreynolds@xxxxxxxxxxxxx>gerryreynolds@xxxxxxxxxxxxx>
>>>
>>> Hi Malcolm,
>>>
>>> Where can you get Silicon steel?? Do they make welding rods out of
>>> this stuff or is there another alloy that would work?? and what
>>> diameter rod should we be looking for??
>>>
>>> Gerry R.
>>
>> Hi Gerry,
>> Silicon steel is the material used in transformer
>> laminations. I can't suggest any shortcuts to getting it any other
>> way sorry. I'm suggesting making the core using discarded transformer
>> laminations. You just want whatever material you are using to have as
>> small a cross-sectional area as small possible to minimize eddy
>> currents. A tale was recounted some years ago of someone who made a
>> ballast core from varnished welding rods which got so hot that the
>> varnish melted. It is questionable whether low-frequency type
>> transformer iron is really that suited to the job anyway as the gap
>> is going to throw step functions at it. A PVC tube full of smashed up
>> N27 ferrites would be a better option. I did this once and built two
>> such cores.
>>
>> Malcolm
>>
>>
>>
>>>
>>>> Original poster: "Malcolm Watts"
> <<mailto:m.j.watts@xxxxxxxxxxxx>m.j.watts@xxxxxxxxxxxx>
>>>>
>>>> Hi Paul,
>>>> Whatever rods you purchase for the core, they have to have
>>>> a very small x-sectional area. They should also not retain much if
>>>> any magnetism after being de-energized (check with a magnet) or they
>>>> will have large hysteresis losses resulting in lots of heating.
>>>> Silicon steel such as used in transformer cores is preferred if you
>>>> can get them.
>>>>
>>>> Malcolm
>>>
>>>
>>>
>>>
>>>
>>
>>
>
>